The present invention relates to a positive working light-sensitive composition which makes it possible to form a presensitized plate for use in making a lithographic printing plate (hereunder referred to as "PS plate"), proof sheets for process printing, figures for overhead projectors or fine resist patterns required for making integrated circuits (IC) of semiconductor elements.
A light-sensitive composition comprising an o-naphthoquinonediazide compound and a novolak type phenol resin has widely been used as an excellent light-sensitive composition for making a lithographic printing plate.
However, the light-sensitive composition is poor in adhesion to a substrate for a printing plate, coating property and abrasion resistance and low in a film strength owing to the property of the novolak type phenol resin which is a main component and therefore it provides only a lithographic printing plate having insufficient printing durability.
On the other hand, as pattern-forming methods used in making electronic parts such as semiconductor elements, magnetic bubble memories and integrated circuits, there have been widely employed methods in which a photoresist sensitive to ultraviolet and visible rays. The photoresists are classified into two groups, one of which is negative working type ones whose exposed portions are made insoluble in a developer by irradiating with light, and the other of which is positive working ones whose exposed portions are, on the contrary, made soluble in a developer. The negative working type ones are superior in sensitivity to the positive working ones and adhesion to a substrate and resistance to chemicals required in wet etching are also excellent. Therefore, the use of negative working resists is one of the mainstreams of photolithography. However, the line width and the distance between lines of patterns become smaller as the degree of integration of semiconductor elements and the packaging density thereof are increased. In addition, dry etching techniques have been adopted as a means for etching substrates. Thus, the photoresists should have high resolution and high resistance to dry etching. For these reasons, positive working photoresists are mainly utilized recently. In particular, there have been exclusively used alkali developable positive working photoresists mainly composed of alkali-soluble novolak resins as disclosed in J.C. Strieter, Kodak Microelectronics Seminar Proceedings, 1976, p. 116, since they are excellent in sensitivity, resolution and resistance to dry etching. There have been proposed many other positive working photoresists such as a light-sensitive compositions comprising a combination of a phenolic resin and an onium salt as disclosed in Journal of Electrochemical Society, Vol. 135, p2322, 1988.
However, it is required to further scale down the size of patterns to thus achieve much higher packaging density and degree of integration accompanied by the recent increase in multifunctionality and high functionality of electronic devices.
More specifically, the size of integrated circuits in their transversal direction is greatly reduced, but the size thereof in the longitudinal direction cannot be reduced so much. Therefore, the ratio of the height of the resist patterns to the width thereof is correspondingly increased. For this reason, it becomes very difficult to restrict the change in size of the resist patterns on a semiconductor wafer having a complicated stepped structure as the scale down of patterns proceeds. In addition, various methods for exposure suffer from problems as the scale down in the minimum size of patterns proceeds. For instance, the exposure by means of light causes interference effect due to light reflected by the stepped portions of the substrate which greatly affects dimensional accuracy. On the other hand, in the exposure by means of an electron beam, the ratio of the height to the width of fine resist patterns cannot be increased because of the proximity effect caused due to backscattering of electrons.
It is found that most of these problems can be eliminated by the use of a multilayered resist system. The multilayered resist system is summarized in Solid State Technology, 74 (1981) and a variety of investigations on the multilayered resist system have been reported. In general, the multilayered resist methods are classified into triple layer resist method and double layer resist method. The triple layer resist method comprises applying an organic film for leveling onto the surface of a stepped substrate, and then applying thereto an inorganic intermediate layer and a resist layer in this order; patterning the resist layer, dry etching the inorganic layer using the patterned resist layer as a mask, and finally patterning the organic leveling layer by O.sub.2 RIE (reactive ion etching) technique using the inorganic layer as a mask to form a desired pattern on the stepped substrate. The investigation of this method has been started from earlier stage since it can essentially utilize techniques conventionally known, but it requires the use of very complicated processes, or since these layers, i.e., an organic film, an inorganic film and an organic film which differ in physical properties from each other are superposed, the intermediate layer is liable to cause cracks or to form pinholes. Contrary to the triple layer resist method, the double layer resist method utilizes a resist having properties of both resist and inorganic intermediate layers in the triple layer resist method, more specifically a resist resistant to oxygen plasma etching and thus the formation of cracks and pinholes can be suppressed. Further, since the number of layers are reduced from 3 to 2, the process can be simplified. However, a conventional resist can be used as the upper resist in the triple layer resist method while, in the double layer resist method, it is required to newly develop a resist excellent in resistance to oxygen plasma.
Under such circumstances, there has been required to develop a highly sensitive positive working photoresist having a high degree of resolution which is excellent in resistance to oxygen plasma and can hence be used as an upper resist in the double layer resist method or the like, in particular an alkaline developable resist which can be used without changing the processes currently employed.
As such a resist, there have been proposed light-sensitive compositions comprising a combination of a conventional o-quinonediazide light-sensitive material and a silicone polymer such as polysiloxane or polysilmethylene which is made alkali-soluble, for instance, those disclosed in J.P. KOKAI Nos. Sho 61-144639, Sho 61-256347, Sho 62-159141, Sho 62-191849, Sho 62-220949, Sho 62-229136, Sho 63-90534 and Sho 63-91654 and U.S. Pat. No. 4,722,881.
All these silicone polymers are made alkali soluble by introduction of phenolic OH group or silanol group (.tbd.Si--OH). The introduction of phenolic groups are very difficult and silicone polymers having silanol groups are not always stable over time.
On the other hand, the positive working photoresist comprising an alkali soluble resin and an onium salt is poor in O.sub.2 RIE property if a phenolic resin is used as an alkali soluble resin, while the positive working photoresist is very difficult to be produced if a polysiloxane/carbonate block copolymer disclosed ih J.P.KOKAI No. Sho 62-136638 is used.